Use of automatic document feeder (ADF) devices in conjunction with imaging equipment is known. Typically, ADFs transport and guide sheet media past a portion of a glass sheet or scan window. A scanning device underlying the scan window optically reads any markings that may be present on the sheet media, and transfers corresponding signals to an imaging system. The imaging system then performs any number of tasks using the signals, such as forming a copy or sending a facsimile of the scanned media, etc.
One aspect of importance to the media scanning process is the proximity of the scanned media to the scan window. The scan window is typically an optically transparent element through which a scanning light source and sensor or the like projects light towards the sheet media as the sheet is moved past the scan window. The scan window also allows for light reflected from the document being scanned to be projected to a photosensor array to thereby allow an image on the scanned sheet to be recorded. The scan window can be a separate component, or it can be a defined portion of a larger platen, as in the case of a flat bed scanner that is provided with an ADF. In the latter case, a document can be scanned by either providing it to the scan window via the ADF, or by placing the document directly on the platen.
In the case where a document is scanned from the ADF, the document is moved past the scan window while the scanning device (which incorporates the scanning light source) is held stationary; in the case where a document is scanned from the platen, the document is held stationary while the scanning device is moved past the document.
Monochrome (i.e., black and white) image scanning is relatively tolerant of varying distance (or “flutter”) between the sheet media and the scan window. In contrast, color image scanning requires a more tightly controlled distance between the media and the scan window, so as to avoid problems in color recognition (i.e., registration). Therefore, ADF devices used in color imaging equipment require a sheet media guidance design that is generally more complex and has a tighter tolerance than that of a monochrome imaging system.
One approach to providing an ADF for use in color imaging involves the use of a transparent sheet guide element. The transparent sheet guide is located within a gap between an overlying feed guide and the underlying scan window. The transparent guide element has a curvature that serves to guide flexible sheet media through the gap during a scanning operation.
During the course of repeated use, the transparent guide element can become soiled or scratched, resulting in unsatisfactory color registration and image quality (i.e., poor copies or facsimiles). Correcting this soiled or scratched condition generally requires a user to remove the transparent guide element from the associated ADF and either clean and reinstall the guide element, or replace it with a new guide element. In any case, the corrective maintenance procedure is both time consuming and undesirable.
Therefore, it is desirable to provide an improved automatic document feeder that avoids the maintenance burdens described above.